A Hong Kong crimelord, Sam (Eric Tsang) decides to plant a number of criminals into the Hong Kong police, including Lau King Ming (Lau). At the same time, the Hong Kong police expel Chan Wing Yan (Leung) - secretly keeping him employed undercover, so that he can infiltrate the criminal underworld. A decade later, when Ming has risen to high office in the police force, and Yan is part of Sam's inner circle, the police and the criminals find out about their respective moles, and begin a highstakes mole-hunt.

Infernal Affairs takes a standard Hong Kong heroic-gunplay action story, and removes the familiar visuals - everybody's gun has the correct number of bullets, and the plot isn't abandoned for some slow-mo, dove-enhanced, flappy-coat indulgences. Surprisingly, this works really well, with the main interest coming from the deceptions the two lead characters are engaged in, and the emotional toll this takes on both of them. There's still a decent amount of action, but it's part of, rather than a substitute for, the plot. Winner of a number of Hong Kong Film awards, this film twists and turns like a good thriller should, and revitalises a familiar genre.